Amoeboflagellate

The heterolobosean pathogen Naegleria fowleri can behave as an amoeba (center) or as a flagellate (right).

An amoeboflagellate is any eukaryotic organism capable of behaving as an amoeba and as a flagellate at some point during their life cycle. Amoeboflagellates present pseudopodia and at least one flagellum, often in separate life stages (as in Naegleria , a human pathogen) ^[1] or in the same stage simultaneously (as in Cercomonas ). ^[2]

Occurrence

The amoeboflagellate cell type has been acquired numerous independent times across the evolution of protists (i.e. primarily unicellular eukaryotes that are not plants, fungi or animals). ^[3] Some examples of protist phyla with amoeboflagellate body types are:

• Cercozoa contains various examples of amoeboflagellates with filose pseudopods, thread-like cell projections also known as filopodia. The cercomonads, glissomonads and paracercomonads behave as amoeboflagellates with two flagella throughout the majority of their life cycle, ^{[2] [4]} and are essential predators of the soil microbiome. ^[5] Among the more basal Cercozoa is Reticulamoeba , an amoeboflagellate with reticulose pseudopods (reticulopodia), filopodia that join into a net-like structure. ^[6]

• Amoebozoa contains several groups of amoeboflagellates with one ^[7] or two flagella ^[8] and lobose pseudopods, which are rounder and more blunt-ended than filopodia. Among them are the myxogastrids, a group of slime molds that behave as amoeboflagellates in various stages of their life cycle. ^[9] Many species of Archamoebae, a more basal group, are anaerobic amoeboflagellates. ^[10] Other examples are the dictyostelians, another group of slime molds, ^[11] and the closely related varioseans, such as Phalansterium . ^[7]

• Breviatea, a small class ^[a] related to animals, fungi and amoebozoans, is composed of anaerobic amoeboflagellates with two flagella. ^{[13] [14]}

• Percolozoa contains amoeboflagellates with lobose pseudopods, but are differentiated by their flat mitochondrial cristae, not tubular as in Amoebozoa. ^{[7] [15]} A popular example is the genus Naegleria , whose members can change shape between an amoeba and a flagellate. ^[1]

The choanoflagellate Salpingoeca rosetta can switch between a swimming (flagellate) stage and a crawling (amoeboid) stage when subjected to a confined space.

The amoeboflagellate phenotype is present in numerous protists that have a crucial phylogenetic position near the origin of animals and fungi, within the vast clade known as Opisthokonta. It has been described in choanoflagellates such as Salpingoeca , filastereans such as Pigoraptor , and even some early-branching fungi such as Sanchytrium , ^[16] but it is absent in animals. ^[3] The two species of Pluriformea have a wide range of cell types, from cellular aggregations to amoeboflagellates. ^[17]

Notes

1. This class belongs to a paraphyletic phylum that is in disuse, known as Apusozoa. ^[12] Although not a phylum itself, it is listed here with other phyla due to comprising an independent clade of organisms.

References

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